Injection molding tools can be used to create high quality optical components such as optical data storage disks. Optical data storage disks have gained widespread acceptance for the storage, distribution and retrieval of large volumes of information. Optical data storage disks include, for example, audio CD (compact disc), CD-R (CD-recordable), CD-ROM (CD-read only memory), DVD (digital versatile disk or digital video disk) media, DVD-RAM (DVD-random access memory), and various types of rewritable media, such as magneto-optical (MO) disks and phase change optical disks. Some newer formats for optical data storage disks are progressing toward smaller disk sizes and increased data storage density. Injection molding tools are also used to create other molded components such as optical components having a high quality reflective surface.
The process of creating high quality injection molded components begins with a mastering process. For example, the creation of optical data storage disks involves making a master disk that has a surface pattern that represents encoded data on the master disk surface. The surface pattern, for instance, may be a collection of grooves that define master pits and master lands. The mastering process is a relatively expensive process in which a photoresist is coated on a master substrate, exposed to electromagnetic radiation to develop a photoresist pattern, and then removed in the non-developed regions. The mastering process may be used not only for pre-recorded disks but also rewritable disks that carry a pattern on the substrate, such as servo tracking or pre-recorded information.
After creating a suitable master, that master can then be used to make a stamper. The stamper has a surface pattern that is the inverse of the surface pattern encoded on the master. For example, to create a stamper suitable for use in an injection molding process, a thin nickel layer can be deposited on the patterned master surface. Then, in an electroplating process, a nickel structural layer can be uniformly plated onto the nickel coated surface of the master. When the electroplating process is complete, the nickel layers can be collectively removed from the master to form a nickel stamper.
The stamper, then, can be inserted within an injection molding tool, and the injection molding tool can be used to injection mold large quantities of molded components such as molded replica disks. The injection molding tool typically includes mirror blocks positioned on both sides of a mold cavity. The stamper can be vacuum drawn against one of the mirror blocks and hot molten thermoplastic can be injected into the mold cavity. The molten thermoplastic conforms to the mold cavity, defining an inverse of the pattern preserved on the stamper. The mirror blocks provide extremely flat surfaces to support the back side of the stamper and to define the non-stamper side of the mold cavity. In addition, the mirror blocks typically include a coolant system to control cooling of the molten thermoplastic.
Upon cooling, the molded component may contain the pattern originally encoded on the master and preserved in the stamper. For example, molded replica disks may contain the data and tracking information that was encoded on the master. Alternatively, the process can be used to create other types of molded components such as high quality reflective components. In that case, the mastering process would define the high quality reflective surface of the molded component that is ultimately created in the injection molding process.